1. Field of the Invention
This invention relates to a bearing assembly including a rolling bearing and a sensor for detecting e.g. rotational angle, temperature or vibration.
2. Description of Related Art
Bearing assemblies of this type are typically used to control e.g. the rotational speed, rotational direction or rotational angle of a motor shaft or an axle of an automobile. The rolling bearing of such a bearing assembly includes a stationary bearing race adapted to be fitted to a stationary member such as a motor housing or an automotive suspension, and a rotary bearing race adapted to be coupled to a rotary shaft. A sensor holder carrying a sensor and wires is supported on the stationary bearing race (see e.g. Japanese Unexamined Patent Application Publication No. 2005-249545).
The sensor holder is typically formed by injection-molding e.g. a thermoplastic resin because such a holder can be formed easily and insulated easily. If the outer race of the rolling bearing is used as the stationary bearing race, the sensor holder is provided with a positioning portion formed with a rib. The positioning portion is fitted into the outer race from one axial end of the outer race until the rib is engaged in a circumferential groove formed in the radially inner surface of the outer race, thus radially positioning the sensor holder relative to the outer race while preventing separation of the sensor holder by the engagement of the rib and the peripheral wall of the circumferential groove. The sensor holder is thus supported by the outer race. (See for example Japanese Unexamined Patent Application Publication No. 2009-074687).
The sensor holder disclosed in Japanese Unexamined Patent Application Publication No. 2009-074687 is an annular member having circumferential ends. The circumferential ends of the sensor holder can be moved toward and away from each other by elastically deforming the sensor holder. When fitting the positioning portion in the outer race, the sensor holder is elastically deformed so that its circumferential ends move toward each other, thereby allowing the rib to be easily engaged in the circumferential groove of the outer race. With the sensor holder supported by the outer race, the sensor holder is fitted in a radially compressed state. Thus, the spring member applies to the sensor holder a spring force that tends to move its circumferential ends away from each other, thereby more rigidly fixing the sensor holder to the outer race.
Typically, the spring member is a C-shaped, snap ring-shaped, circular member which can be fitted in an annular groove formed in the sensor holder so as to extend between the circumferential ends of the sensor holder and having circumferential ends. When the spring member is fitted in the annular groove with its circumferential ends located close to each other, the spring member elastically pushes the sensor holder radially outwardly, and the spring member can be fixed to the sensor holder.
In a different arrangement, with the rib fitted in the circumferential groove, a spring member is pushed into between circumferential ends of the sensor holder and secured to the sensor holder. This spring member comprises free end portions adapted to be deflected when the sensor holder is pushed into between the circumferential ends of the sensor holder, and an intermediate portion connecting together the free end portions. Using the elastic force when the free end portions are deflected, the circumferential end portions of the sensor holder are biased away from each other. This elastic force also serves to more strongly fix the spring member
In Japanese Unexamined Patent Application Publication No. 2009-074687, to easily secure the spring member to the sensor holder, the spring member is provided with circumferential half-split elastic recovery portions having a split structure, like a snap ring shape or a split groove shape caused by the free end portions.
However, in the spring member disclosed in Japanese Unexamined Patent Application Publication No. 2009-074687, the sensor holder is strongly fixed depending on the elastic recovery characteristic of both of the elastic recovery portions having the split structure. The elastic recovery portion itself has the limitation of increasing the elastic recovery characteristic. As such, when a diameter of the sensor holder is increased corresponding to an increase in diameter of the outer race, there is a possibility of being insufficient to strongly fix the sensor holder. For example, since a bending radius of the concentric C-shaped, snap ring-shaped spring member having the circumferential half-split elastic recovery portions becomes large, the spring forces transferred to the opposite end sides of the sensor holder have a tendency toward reduction. Further, the spring member, in which opposite free end portions are formed as the circumferential half-split elastic recovery portions, is formed by injection molding. As such, the spring member lacks the elastic recovery characteristic of the free end portions, and thus there is no choice but to increase the elastic recovery characteristic within a range in which injection molding synthetic resins are selected.